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%I #6 Jan 06 2020 12:54:16
%S 1,3,33,979,54801,4932051,651030673,118487582403,28437019776609,
%T 8701728051642211,3306656659624040001,1527675376746306480243,
%U 843276807963961177093873,548129925176574765111017139,414386223433490522423928956721,360516014387136754508818192346851
%N a(n) = (A000522(2*n) + 1)/2.
%H Andrew Howroyd, <a href="/A086894/b086894.txt">Table of n, a(n) for n = 0..100</a>
%F a(n) = (1 + (2*n)!*Sum_{k=0..2*n} 1/k!)/2. - _Andrew Howroyd_, Jan 05 2020
%o (PARI) a(n)={(1 + sum(k=0, 2*n, (2*n)!/k!))/2} \\ _Andrew Howroyd_, Jan 05 2020
%Y Cf. A000522.
%K nonn
%O 0,2
%A _Vladeta Jovovic_, Aug 22 2003
%E Terms a(11) and beyond from _Andrew Howroyd_, Jan 05 2020